Talvivaara Mining’s bioheap leaching technology for extracting metals such as nickel, copper, cobalt, and zinc from sulphidic ore or waste materials is both cost-effective and environmentally friendly. The technology will be used at a new mine currently being built in northern Finland to exploit Europe’s largest sulphide nickel deposit.
Microbes are opening up exciting new frontiers in mining, and can be expected to play a growing role in the low-cost, efficient, and clean discovery, extraction, and processing of minerals. Their use in extracting minerals is based on their ability to oxidise ferrous iron to ferric iron, and sulphur to sulphates. The resulting oxidising conditions dissolve the target metals out of the ore into a solution, from which they can be recovered using conventional methods.
Talvivaara Mining has taken this basic principle and developed a new bioheap leaching process to create and maintain the ideal environment for this type of bacterial activity – through careful heap design and the efficient management of internal heap parameters, such as temperature, aeration, water, nutrients, and acid balance.
Proven in practice
The new Talvivaara method addresses the need to maintain a variety of microbial populations and manage their growth rates and guarantee the temperatures required for enhanced primary sulphide mineral leaching. As these temperatures need to be in excess of 50 °C for successful bioleaching, the mesophile population required for early heat generation needs to be replaced by a thermophile population for sustained heat generation at the appropriate point.
Factors such as micro-organism dynamics, adaptation and succession rates, as well as ore energy-generating capacity, have also been addressed, as has the need to optimise the rate of leaching and understand what can inhibit or retard microbial growth.
The success of the technology has been proved at a 17,000 t/a demonstration plant built at the site of the new Talvivaara mine, using a heap inoculated with indigenous mesophilic and thermophilic bacteria collected from the site. Temperatures rapidly reached in excess of 50 °C and were maintained during the winter, and high levels of nickel and zinc have been successfully extracted, together with copper and cobalt.
Positive for the environment
In addition to attractive cost benefits, Talvivaara’s bioheap leaching technology also offers valuable environmental advantages, as bacteria consume carbon dioxide and convert it into organic material that can be returned to the carbon cycle. No noxious gases are generated, and all the sulphides are converted into water-soluble sulphates.
|Talvivaara’s bioheap leaching produces metal ions, acid, and inert rock free of sulphide mineralisation. Metals can be removed by electrolysis and/or precipitation, and any acid generated is circulated back to the bioleaching process.